An optical disk apparatus, such as a magneto-optical disk apparatus, for recording data and reading out the recorded data by means of a semiconductor laser has been used extensively as an information recording/reproducing apparatus for recording and saving, for example, image data of a large volume.
With an erasable (overwritable) optical disk, such as a magneto-optical disk, data is recorded/reproduced sector by sector provided in the recording track. Each sector is assigned with a physical address (pit) by means of injection molding or 2P process when the disk is manufactured.
An optical disk may have a defect due to a flaw on the substrate or a failure, such as a pin hole in the recording film, caused when molding the optical disk substrate, or a surface flaw of the optical disk substrate caused during the use. If a sector has such a defect, data can not be recorded/reproduced into/from this defective sector correctly. Thus, before the use (delivery) or during the use of the optical disk, a defective sector in the optical disk is detected so as not to use the detected defective sector when actually recording/reproducing data.
In order to record/reproduce data by avoiding the defective sector, the optical disk is provided with defect management areas (hereinafter, abbreviated to DMAs) into which information (defect management information) as to an address of the defective sector and the structure of the optical disk is recorded.
An optical disk employed as a recording medium for the foregoing optical disk apparatus should comply with the ISO (International Standards Organization) standard and the AS-MO (Advanced Storage-Magneto Optical Disk) standard.
FIG. 11 shows a physical alignment of the DMAs in an optical disk in compliance with the 90-mm media ISO standard.
A user data area 11E used in recording user data, such as image information, is sandwiched by four DMAs in total: DMAs 11A and 11B in the inner side and DMAs 11C and 11D in the outer side.
FIG. 12 shows a physical alignment of the DMAs in an optical disk in compliance with the AS-MO standard. In the AS-MO standard, both lands and grooves in the optical disk are used as recording tracks to increase a recording density.
Like the medium shown in FIG. 11, four DMAs are also provided in the optical disk of FIG. 12. Outer grooves of a data area 12E are allocated as a DMA 12A and outer lands of the data area 12E are allocated as a DMA 12B. Likewise, inner grooves and lands of the data area 12E are allocated as DMAs 12C and 12D, respectively. Thus, according to the AS-MO standard, the DMAs 12A and 12B or the DMAs 12C and 12D are aligned alternately in every other track.
Here, four DMAs are provided to ensure reliability of the optical disk. More precisely, if a defect is caused in the DMA due to a surface flaw or the like of the optical disk, the management information can no longer be recorded or reproduced, thereby making the optical disk totally inoperable. Therefore, the same defect management information is recorded into four DMAs to ensure safety.
An optical disk apparatus reproduces the defect management information recorded in the DMAs at the start-up and stores the same in its memory, and refers to the stored information when recording or reproducing data later, thereby avoiding the use of a defective sector.
FIGS. 13 and 14 show flowcharts detailing actions when an optical disk apparatus employing an optical disk in compliance with the AS-MO standard reproduces/records defect management information from/into the DMAs 12A–12D.
FIG. 13 shows reproduction of the defect management information. The reproduction of the defect management information starts when an optical disk is inserted into the optical disk apparatus. That is, the head of the DMA 12A positioned in the outer side is accessed (S21) followed by tracking servo in the groove track (S22). Then, reproduction from the DMA 12A starts from the outer side to the inner side (S23), after which whether the defect management information has been reproduced correctly or not is judged (S24). If the defect management information recorded in the DMA 12A has been reproduced correctly, the reproduction is terminated.
However, if the defect management information recorded in the DMA 12A has not been reproduced correctly by a defect or the like on the optical disk, the head of the DMA 12B also positioned in the outer side is accessed (S25) followed by tracking servo in the land track (S26) Then, reproduction from the DMA 12B starts from the outer side to the inner side (S27). If the defect management information has not been reproduced correctly again, reproduction from the DMA 12C and DMA 12D (S29–S36) is carried out as necessary in the same manner.
FIG. 14 shows recording of the defect management information. When a new defective sector is detected in the data area, new defect management information is generated (not shown), and as is with the reproduction, the head of the DMA 12A is accessed (S37) followed by tracking servo in the groove track (S38). Then, recording into the DMA 12A starts from the outer side to the inner side (S39). Subsequently, the head of the DMA 12B also positioned in the outer side is accessed (S40) followed by tracking servo in the land track (S41). Then, recording into the DMA 12B starts from the outer side to the inner side (S42). Thereafter, recording into the DMAs 12C and 12D both positioned in the inner side is carried out sequentially in the same manner (S43–S48). Consequently, the new defect management information is recorded into four DMAs unconditionally.
However, the foregoing arrangement of the conventional optical disk has the following problem. That is, the defect management information recorded in the DMAs is read out only after the optical disk is inserted into the optical disk apparatus, and there is no way to give the same to the optical disk apparatus in advance. Moreover, should a defect be caused in all the four DMAs, information can not be reproduced from any of the DMAs, thereby making the optical disk totally inoperable. Under these conditions, there has been an increasing need to ensure reliability of the defect management information.
The ISO standard sets forth the recording track pitch as 1.6 μm. Thus, if a defect of some micrometers wide is caused in the DMA 11A, more than one recording track becomes defective, and when this happen, an error can not be corrected. Thus, there is a problem that, because the DMA 12A out of four DMAs is no longer operable, the reliability of the defect management information is decreased.
In addition, if a defect is caused at the boundary between two adjacent DMAs, such as the DMAs 11A and 11B, there arises another problem that two out of four DMAs become inoperable at the same time.
The above problem is more serious with the optical disk in compliance with the AS-MO standard. More precisely, this type of optical disk adopts a recording method, by which information is recorded into both the lands and grooves constituting the recording track so as to increase a recording density. However, because the track pitch is as small as 0.6 μm, even a microscopic defect may possibly lie off more than one recording track.
In addition, assume that the DMAs 12A and 12B are provided in the grooves and lands alternately in every other track, for example. Then, the DMAs 12A and 12B are adjacent to each other throughout the recording track. Thus, if a defect such that lies over more than one track is caused in anywhere in the DMA 12A or 12B, both the DMAs 12A and 12B become totally inoperable at the same time.
With the optical disk apparatus employing the optical disk in compliance with the AS-MO standard, as has been discussed, the recording/reproducing into/from the DMA 12B is carried out following the recording/reproducing into/from the DMA 12A, and an access action is necessary in order to move from the last sector of the DMA 12A to the first sector of the DMA 12B. This raises a problem that the time required for the defect management information recording/reproducing is extended undesirably, thereby decreasing a processing rate of the optical disk apparatus.